Edwin, we got two websites and we need the users to be able to login on both of the website using the the same login.

one is spanish website and other one is english one.

now, what i am looking at it is. we want to be able to send out weekly email newsletter to the users of the site... but we want to make sure the users of Spanish site recieve the spanish newsletter and users of english site recieves only the english one.

Let me know your thoughts please.

Thanks.

With JMS you can share the users.
So they could be able to login in both website.

In general the newsletter could use the language assigned to the user.
So you should perhaps investigate the language code that is assinged to each user - whatever the website where it is logged. The customer could be logged on the english site and receve their newsletter in spanish because their profile is recorded with spanish.

Thanks for the reply Edwin. but we are having the same language in the backend and frontend as well... the only thing which is going to be different is the newsletter language.

Let me know please?

As you say this specific to the NewsLetter extension that you are using then check there.
As I don't know which NewsLetter you are using I am not able to answer you.
You have to analyze the code of this extension to see how it works.